Ethernet Explained

• Ethernet is a network protocol that controls how data is transmitted over a LAN.
• It's referred to as the Institute of Electrical and Electronics Engineers (IEEE) 802.3 Standard.
• It supports networks built with coaxial, twisted-pair, and fiber-optic cabling.
• The original Ethernet standard supported 10 Mbps speeds, but the latest supports much faster gigabit speeds.
• Ethernet uses CSMA/CD & CSMA/CA access methodology.

Why Is Cabling Important?

• Foundation of the Physical Network: Cables form the physical medium through which all wired data travels — without reliable cabling, no network communication is possible.
• Performance: The type of cable directly determines maximum speed, bandwidth, and latency of the network.
• Reliability: Poor or incorrect cabling is the #1 cause of intermittent network failures and downtime.
• Scalability: Choosing the right cable standard today (e.g. Cat 6a over Cat 5e) future-proofs the network for higher speeds.
• Cost Impact: Cabling infrastructure is expensive to replace — choosing wisely upfront saves significant long-term costs.
• Security & Safety: Cable choice affects vulnerability to signal interception and must meet building fire codes (plenum-rated).

Network Cable Attributes

• Bandwidth Rating: The number of bits per second that can be transmitted across a medium. (Example: 1 Gbps)
• Maximum Segment Distance: The maximum distance that the medium can reliably carry data before it must be regenerated.
• Interference Susceptibility: How susceptible the medium is to electromagnetic interference (EMI) or crosstalk.
  • Example: A UTP cable running alongside fluorescent lights or a microwave oven picks up electromagnetic noise, causing data errors and retransmissions.
• Security: How easily can someone "tap" the cable to intercept the signal.
  • Example: Copper cables emit faint electrical signals (emanations) that can be captured with special equipment. Fiber optic cables don't emanate signals, making them much harder to tap.

IEEE 802.3 Ethernet Standards

IEEE 802.3 is the standard that defines how Ethernet works — it's maintained by the Institute of Electrical and Electronics Engineers (IEEE) and is the foundation for virtually all wired local area networks today.

• Defines both the Physical (Layer 1) and Data Link MAC Sub-Layer (Layer 2) of the OSI Model.
• Covers everything from cable specifications and signalling to how devices access the shared medium.
• Naming Convention Format: Speed + Baseband/Broadband + Type of Cable

Coaxial Cabling

Antiquated technology used in the 1980s. Coaxial cables are rarely used today, except for cable modem connections.

Categorized as Radio Grade (RG)

• RG-6: Modern cable TV and broadband cable modems.
• RG-8: Early 10Base5 "Thick-net" Ethernet networks.
• RG-58: Early 10Base2 "Thin-net" Ethernet networks.
• RG-59: Closed-circuit TV (CCTV) networks.

Metallic shield helps protect against electromagnetic interference (EMI).

Coaxial Cable Connectors

F-Connector

• Screw-on connection
• RG-6 Cable TV and Broadband Cable Applications

BNC Connector

• Tension spring twist-on connection
• RG-8 "Thick-net" and RG-58 "Thin-net" network applications

Twisted Pair Copper Network Cabling

• 4 Twisted Pairs of Wires with RJ-45 Connector
• Balanced pair operation — equal & opposite signals (+/−)
• Why are they twisted? To help reduce interference:
  • Crosstalk: When signals from one wire pair "leak" into an adjacent pair — twisting the pairs at different rates ensures each pair's interference cancels out, keeping signals clean.
  • Noise (EMI): External electromagnetic sources (motors, fluorescent lights, power cables) create interference. Because each twist reverses the wire orientation, the noise picked up on one half of the twist is equal and opposite to the next half — they cancel each other out. More twists per inch = better noise cancellation.
• Security concerns: Signal Emanations
• 100 Meters Maximum Distance: Signal Attenuation

Shielded vs. Unshielded & EMI

Electromagnetic Interference (EMI): The disruption of an electronic device when it's near an electromagnetic field caused by another device (manufacturing equipment, microwave ovens, etc.).

Twisted Pair Standards

Cat: Copper Cabling Standard

Roles of Twists & Other Connectors

Increased Twists Per Inch:

• Reduces Crosstalk
• Increases Signals
• Supports Faster Speeds

Other Copper Cable Connectors

• DB-25: 25-pin connection — previously used for serial printer connections
• DB-9: 9-pin connection — used for serial connections on networking devices
• RJ-11: 4-pin connection — used for telephone connections

TIA/EIA 568A & 568B Wiring Standards

Industry standards defined by the Telecommunications Industry Association (TIA) and the Electronic Industries Alliance (EIA) that specify the pin-to-wire colour assignment for RJ-45 connectors on UTP cables.

568A — Pin Order

1. White/Green
2. Green
3. White/Orange
4. Blue
5. White/Blue
6. Orange
7. White/Brown
8. Brown

Originally used in U.S. government & phone systems

568B — Pin Order Recommended

1. White/Orange
2. Orange
3. White/Green
4. Blue
5. White/Blue
6. Green
7. White/Brown
8. Brown

Most widely used in commercial & enterprise networks today

Straight-Through & Crossover Cables

Crossover Cable

Connecting "Like" Devices

• Router to Router
• Computer to Computer
• Switch to Switch

Uses 568A on one end, 568B on the other

Straight-Through Cable

Connecting "Unlike" Devices

• Computer to Switch
• Switch to Router
• Computer to Router

Uses the same standard (568B) on both ends

Which Twisted Pairs Are Used?

The Plenum

• The plenum is the open space above the ceiling or below a raised floor.
• A "plenum space" enables air circulation — provides pathways for heated/air-conditioned and return airflows at a higher pressure than normal.
• All network cabling placed in the plenum should be "plenum-rated."

Fire Hazards & Plenum-Rated Cables

Fiber Optic Network Cabling

Glass or plastic fiber that carries light (photons).

• High Bandwidth: Photons travel faster than electrons
• Long Distances: Less attenuation
• Immune to Electromagnetic Interference (EMI)
• Doesn't Emanate Signals — more secure

Multi-mode vs. Single-mode Fiber

Multi-mode Fiber (MMF)

• Shorter Distances (LAN / Building-to-Building)
• Up to 2 Kilometers
• Many photons travel at once, bouncing off walls — reduces distance and speed
• Larger Core: 50 to 62.5 microns
• Less expensive

Single-mode Fiber (SMF)

• Longer Distances (WAN / Across Town)
• Up to 200 Kilometers
• A single direct photon travels through — greater distance and speed
• Smaller Core: 8 to 10 microns
• More expensive

Fiber Optic Cable Connectors

• Lucent Connector (LC): Small form-factor, flange on top (like RJ-45). Used in MMF & SMF gigabit and 10-gigabit networks.
• Straight Tip (ST): BNC-style with half-twist bayonet lock. Was used in MMF networks — not common anymore.
• Subscriber Connector (SC): Square push-pull connector. Common in MMF & SMF gigabit Ethernet.
• MTRJ: Similar to RJ-45, houses two fiber cables. Designed for MMF networks.

Why Use Fiber?

• Fiber cable is more expensive than twisted pair, as is the equipment
• But you can perform much longer cable runs (100 m copper vs. up to 200 km fiber)
• Decreased network equipment costs (fewer switches, routers needed for long runs)
• Immune to EMI and signal emanations
• Lower signal attenuation — more reliable and secure
• Costs are steadily decreasing as more people adopt fiber

Networking Cable Selection Criteria

• Cost Constraints: What is your budget?
• Transmission Speed Requirements: How fast does your network need to be?
• Distance Requirements: Electrical signals degrade relatively quickly (100 m). Fiber can transmit over long distances.
• Noise & Interference Immunity: Interference is all around us — power cables, microwaves, mobile phones, motors, etc. Consider Crosstalk, EMI, and Security.

Week 3 Summary

• Cable Attributes: Bandwidth, Distance, Interference, Security
• IEEE 802.3: Naming convention — Speed + Base/Broad + Cable Type
• Twisted Pair: Cat 3 through Cat 7 — UTP vs STP
• Coaxial: RG-6, RG-8, RG-58, RG-59 — F-Connector & BNC
• Wiring Standards: 568A & 568B — Crossover vs Straight-Through
• Plenum: Fire safety — Teflon, FEP, Low-Smoke PVC coatings
• Fiber Optic: MMF (2 km) vs SMF (200 km) — LC, ST, SC, MTRJ connectors
• Cable Selection: Cost, Speed, Distance, Noise Immunity